Add support for having different forkid values in SigHashType

Summary:
This implements support for different fork id values as per https://github.com/bitcoincashorg/spec/blob/master/replay-protected-sighash.md .

Depends on D1189

Test Plan: Updated untitests to check the new feature.

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Subscribers: jasonbcox, teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1190